Inhibitor of granulocyte-macrophage colony formation in plasma of mice rendered aplastic by allogeneic lymph node cells.

Sublethally irradiated CBA/J mice injected with lymph node cells (LNC) of C3H/He mice exhibit aplastic anemia within 3 weeks. Aplastic anemia plasma (AAP) from these mice was found to inhibit granulocyte-macrophage colony (GM-CFU) formation. This inhibitory action was not strain specific and was not generated in donor:host combination involving other strains. AAP also inhibited the formation of colonies derived from leukemic cell lines. Though this activity inhibited GM-CFU, it did not affect erythroid colony formation. Two experiments were performed to examine the mechanism of inhibition. Superoptimal concentrations of recombinant mouse granulocyte-macrophage colony-stimulating factor (GM-CSF) did not reverse AAP-induced inhibition of colony formation. Bone marrow cells preincubated with AAP for 24 h and washed were unchanged in their ability to form GM-CFU colonies. Thus, the inhibitory activity acted neither as a competitive nor a cytotoxic agent. Interferons and certain prostaglandins, known to inhibit colony formation, were not found in active concentrations in AAP. The inhibitory activity of AAP was heat stable, nondialyzable, inextractable with chloroform, precipitable with 50% ammonium sulfate, and had a molecular weight of 100,000 daltons. In contrast, control plasma from mice given only sublethal irradiation and injected with saline had significantly less inhibitory activity, which was not heat stable and was extractable with chloroform. Thus, LNC in certain host mouse strains generate a plasma activity that can inhibit the formation of normal and leukemic GM-CFU colonies.